195 research outputs found
From Molecular Cores to Planet-forming Disks: An SIRTF Legacy Program
Crucial steps in the formation of stars and planets can be studied only at mid‐ to far‐infrared wavelengths, where the Space Infrared Telescope (SIRTF) provides an unprecedented improvement in sensitivity. We will use all three SIRTF instruments (Infrared Array Camera [IRAC], Multiband Imaging Photometer for SIRTF [MIPS], and Infrared Spectrograph [IRS]) to observe sources that span the evolutionary sequence from molecular cores to protoplanetary disks, encompassing a wide range of cloud masses, stellar masses, and star‐forming environments. In addition to targeting about 150 known compact cores, we will survey with IRAC and MIPS (3.6–70 μm) the entire areas of five of the nearest large molecular clouds for new candidate protostars and substellar objects as faint as 0.001 solar luminosities. We will also observe with IRAC and MIPS about 190 systems likely to be in the early stages of planetary system formation (ages up to about 10 Myr), probing the evolution of the circumstellar dust, the raw material for planetary cores. Candidate planet‐forming disks as small as 0.1 lunar masses will be detectable. Spectroscopy with IRS of new objects found in the surveys and of a select group of known objects will add vital information on the changing chemical and physical conditions in the disks and envelopes. The resulting data products will include catalogs of thousands of previously unknown sources, multiwavelength maps of about 20 deg^2 of molecular clouds, photometry of about 190 known young stars, spectra of at least 170 sources, ancillary data from ground‐based telescopes, and new tools for analysis and modeling. These products will constitute the foundations for many follow‐up studies with ground‐based telescopes, as well as with SIRTF itself and other space missions such as SIM, JWST, Herschel, and TPF/Darwin
From Molecular Cores to Planet-forming Disks: A SIRTF Legacy Program
Crucial steps in the formation of stars and planets can be studied only at
mid-infrared to far-infrared wavelengths, where SIRTF provides an unprecedented
improvement in sensitivity. We will use all three SIRTF instruments (IRAC,
MIPS, and IRS) to observe sources that span the evolutionary sequence from
molecular cores to protoplanetary disks, encompassing a wide range of cloud
masses, stellar masses, and star-forming environments. In addition to targeting
about 150 known compact cores, we will survey with IRAC and MIPS (3.6 to 70
micron) the entire areas of five of the nearest large molecular clouds for new
candidate protostars and substellar objects as faint as 0.001 solar
luminosities. We will also observe with IRAC and MIPS about 190 systems likely
to be in the early stages of planetary system formation(ages up to about 10
Myr), probing the evolution of the circumstellar dust, the raw material for
planetary cores. Candidate planet-forming disks as small as 0.1 lunar masses
will be detectable. Spectroscopy with IRS of new objects found in the surveys
and of a select group of known objects will add vital information on the
changing chemical and physical conditions in the disks and envelopes. The
resulting data products will include catalogs of thousands of previously
unknown sources, multiwavelength maps of about 20 square degrees of molecular
clouds, photometry of about 190 known young stars, spectra of at least 170
sources, ancillary data from ground-based telescopes, and new tools for
analysis and modeling. These products will constitute the foundations for many
follow-up studies with ground-based telescopes, as well as with SIRTF itself
and other space missions such as SIM, JWST, Herschel, and TPF.Comment: (22 pages, 10 figures, PASP in press
The Spitzer ice legacy: Ice evolution from cores to protostars
Ices regulate much of the chemistry during star formation and account for up
to 80% of the available oxygen and carbon. In this paper, we use the Spitzer
c2d ice survey, complimented with data sets on ices in cloud cores and
high-mass protostars, to determine standard ice abundances and to present a
coherent picture of the evolution of ices during low- and high-mass star
formation. The median ice composition H2O:CO:CO2:CH3OH:NH3:CH4:XCN is
100:29:29:3:5:5:0.3 and 100:13:13:4:5:2:0.6 toward low- and high-mass
protostars, respectively, and 100:31:38:4:-:-:- in cloud cores. In the low-mass
sample, the ice abundances with respect to H2O of CH4, NH3, and the component
of CO2 mixed with H2O typically vary by <25%, indicative of co-formation with
H2O. In contrast, some CO and CO2 ice components, XCN and CH3OH vary by factors
2-10 between the lower and upper quartile. The XCN band correlates with CO,
consistent with its OCN- identification. The origin(s) of the different levels
of ice abundance variations are constrained by comparing ice inventories toward
different types of protostars and background stars, through ice mapping,
analysis of cloud-to-cloud variations, and ice (anti-)correlations. Based on
the analysis, the first ice formation phase is driven by hydrogenation of
atoms, which results in a H2O-dominated ice. At later prestellar times, CO
freezes out and variations in CO freeze-out levels and the subsequent CO-based
chemistry can explain most of the observed ice abundance variations. The last
important ice evolution stage is thermal and UV processing around protostars,
resulting in CO desorption, ice segregation and formation of complex organic
molecules. The distribution of cometary ice abundances are consistent with with
the idea that most cometary ices have a protostellar origin.Comment: 48 pages, including 19 figures. Accepted for publication in Ap
The Mid-Infrared Extinction Law in the Ophiuchus, Perseus, and Serpens Molecular Clouds
We compute the mid-infrared extinction law from 3.6-24 microns in three
molecular clouds: Ophiuchus, Perseus, and Serpens, by combining data from the
"Cores to Disks" Spitzer Legacy Science program with deep JHKs imaging. Using a
new technique, we are able to calculate the line-of-sight extinction law
towards each background star in our fields. With these line-of-sight
measurements, we create, for the first time, maps of the chi-squared deviation
of the data from two extinction law models. Because our chi-squared maps have
the same spatial resolution as our extinction maps, we can directly observe the
changing extinction law as a function of the total column density. In the
Spitzer IRAC bands, 3.6-8 microns, we see evidence for grain growth. Below
, our extinction law is well-fit by the Weingartner & Draine
(2001) diffuse interstellar medium dust model. As the extinction
increases, our law gradually flattens, and for , the data are
more consistent with the Weingartner & Draine model that uses
larger maximum dust grain sizes. At 24 microns, our extinction law is 2-4 times
higher than the values predicted by theoretical dust models, but is more
consistent with the observational results of Flaherty et al. (2007). Lastly,
from our chi-squared maps we identify a region in Perseus where the IRAC
extinction law is anomalously high considering its column density. A steeper
near-infrared extinction law than the one we have assumed may partially explain
the IRAC extinction law in this region.Comment: 38 pages, 19 figures in pre-print format. Accepted for publication in
ApJ. A version with full-resolution figures can be found here:
http://peggysue.as.utexas.edu/SIRTF
VLT-ISAAC 3-5 micron spectroscopy of low-mass young stellar objects: prospects for CRIRES
We present results from an extensive spectroscopic survey in the 3-5 micron
wavelength region of low-mass young stellar objects using VLT-ISAAC. Medium
resolution spectra (R ~ 1000-10000) of young embedded stars in the mid-infrared
allow for detailed studies of ro-vibrational lines from molecular gas,
interstellar ices and Polycyclic Aromatic Hydrocarbons (PAHs). By taking
advantage of this wide range of molecular tracers available within a few
spectral settings, the survey has helped to constrain the chemical evolution of
cold molecular material in low-mass star forming regions as well as the physics
of disks surrounding protostars. In this contribution, we will review the
various spectral diagnostics of molecular material, which require ground-based
high resolution infrared spectroscopy. The importance of a high resolution
spectroscopic capability as will be offered by CRIRES is discussed in the
context of the physics and chemistry of low-mass star formation.Comment: 11 pages, Proceedings of the ESO workshop: "High Resolution Infrared
Spectroscopy in Astronomy", H.U. Kaufl, R. Siebenmorgen & A. Moorwood (eds.),
Garching, Germany, November 200
Spatial mapping of ices in the Ophiuchus-F core. A direct measurement of CO depletion and the formation of CO_2
Wetensch. publicati
- …